Electrical measuring instrument.



W. H. PRATT.

ELECTRICAL MEASURING INSTRUMENT.

APPLICATION FILED AUG.14, 1911.

1,077,429. Patented N0v.4,1913.

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UNITED snares PATENT OFFICE.

WILLIAM H. PRATT, OF LYNN, MASSACHUSETTS, .ASSIGNOR T0 GENERAL ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

ELECTRICAL MEASURING INSTRUMENT.

Application filed. August 14, 1911. 7 Serial No. 643,843.

circuit systems, such as multiphase systems or three-wire systems eitheralternating or direct current. For such purpose, it has been customaryheretofore to employ two.

elements connected in separate circuits and cooperating to actuate aslngle indicating .or recording device.

The object of my invention is to provide simple and effective means forpreventing the leakage flux of one element from affecting the otherelement and thereby for assuring the accuracy of the instrument. Certainarrangements have been resorted to heretofore for this purpose. In onesuch arrangement a magnetic shield in the shape of an iron member hasbeen interposed between the two elements. This is efiiective butincreases the weight of the instrument. Another arrangement which hasbeen used in instruments of the zero deflection type, such asdynamometers, has been to place the coils of one element in planes atright angles to those of the other element so as to make the windings ofthe two elements mutually non-inductive. Such an arrangement does nothowever entirely prevent interference in instruments in which themovable members deflect from the zero position, as in ordinary ammetersand wattmeters.

I obtain the desired result, or protection against disturbing leakagefluxes, by providing on each element an auxiliary wlndlng properlyarranged to neutrallze the effect on that element of leakage flux fromthe other element.

My invention will best be understood by reference to the accompanyingdrawing, which shows diagrammatically an instrument arranged inaccordance with my invention.

In the drawing 1, 2 and 3 represent three conductors of a multicircuitsystem. This system may be either three-phase, or twophase, or athree-wire single phase or direct Specification of Letters Patent.

Patented Nov. 4:, 1913.

current system. Lamps or other current consuming devices are indicatedat E. The indicating instrument shown diagrammatically consists of twoelements each having a stationary actuating coil A or A and a movablecoil B or B.. The coils A and A are connected in conductors 1 and 3,re-.

spectively, in series with the load and the coils B and B are connectedin shunt to the load between conductors l and 2 and conductors 2 and '3,respectively, with resistances b and b respectively in series with them.The connections shown .are those of .a wattmeter but it will beunderstood that my invention is not limited to wattmeters. The movablecoils B B are carried on a common shaft C, which carries an indicator orneedle D moving over suitable scale d.

In order to neutralize the effect-of leakage fiux from the stationarycoil A on the movable coil B of the other element, I pro vide theauxiliary winding a which is of few turns compared to the main winding A(in the drawing this auxiliary winding is shown as consisting of asingle turn) connected in series with winding A and located in inductiverelation to the moving coil B in the same plane as coils A and A or in aplane parallel thereto. It will be seen that if the coil a is properlyproportioned and properly located, it will completely neutralize theefiect of leakage flux from coil A on coil B since the currents in thetwo coils A and a are always the same. A similar coil a is placed overor adjacent to the coil A in inductive relation to coil B so as toneutralize the efiect thereon of leakage flux from the coil A of theother element. Thus, all interference between the two elements isprevented.

I do not desire to limit myself to the particular construction andarrangement of parts shown and described but aim in the appended claimsto cover all modifications which are within the scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is 1. In an electrical measuring instrument two elements, eachcomprising a stationary and a movable winding, a mechanical connectionbetween the movable windings, and auxiliary windings in inductiverelation to one of the windings of each element and arranged toneutralize the eiiect upon said last mentioned winding of the leakageflux of the other winding of the other element respectively.

2. In an electrical measuring instrument, two elements, each comprisinga movable member and a stationary actuating winding therefor, amechanical connect-ion between said movable members, and auxiliarywindings, each in circuit with the stationary winding of one element andneutralizing the effect of its leakage flux on the movable member of theother element.

3. In an electrical measuring instrument for multicircuit systems, twoelements, each comprising a movable member and a stationary actuatingwinding therefor, a mechanical connection between the movable members,said windings being connected in different circuits, and auxiliarywindings of few turns compared to said actuating windings each ininductive relation to the movable member of one of said elements andCopies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents,

connected in series with the actuating windlng of the other element.

4. In an electrical measuring instrument,

two elements, each comprising a stationary and a movable me1nber,amechanical con nection between said movable members, an actuatingwinding and an auxiliary winding being comprised in one member of eachelement, the auxiliary winding having few ampere turns compared to theactuating winding, and the auxiliarywinding of one element beingconnected in circuit with the actuating winding of the other elementandacting to neutralize the effect of its leakage flux on the firstelement.

In witness whereof, I have hereunto set my hand this 11th day of August,1911.

- WVILLIAM H. PRATT. lVitnesses:

JOHN A. MoMANUs, Jr.,

O'rro F. PERssoN.

Washington, D. G. a

